1. Field of Invention
The invention is useful in an adapter for connecting a self-contained camera with automatic exposure control or a light meter to an image-forming optical system, such as a microscope. The system directs the portion of the image outside of the film format to the exposure control port of the camera so that the light needed for the picture is not appreciably reduced while at the same time providing as much light as possible to the camera's automatic exposure control mechanism.
2. Description of Prior Art
Prior art adapters for coupling automatic exposure control cameras to optical instruments have been designed to remove light from the image-forming instrument, which would normally lie outside of the film format in the camera for use in operating the camera's automatic exposure control mechanism. Typical of these devices are those shown in U.S. Pat. Nos. 3,898,678; 3,900,858; and 3,976,368. The complexity of and number of operative elements in the devices described in these patents result in unnecessarily high production costs and difficulty in operating the adjustable peripheral light extracting means during the photographing process. An extremely important limitation of the prior art devices is that they disclose structure capable of withdrawing only portions of the light from the image-forming instrument which lie outside of the film format of the camera for use in activating the exposure control mechanism within the camera. This can be ineffective in part, because the intensity of light being measured by such a device may not be indicative of the intensity of light received from the object being photographed. The operator in these situations is required to adjust the light extracting device to both maximize the amount of light being extracted from the periphery of the photographic field and, to the extent possible, find a representative light intensity within that peripheral image. Further, there is quite often inadequate light eminating from the object to be photographed to operate the camera's exposure control mechanism without either recalibration of the camera's system from its design range or increasing the intensity of light on the subject being photographed, which can have negative effects both on the object being photographed and the appearance of the image being focused within the camera format.
One of the problems dealt with in the prior art is that the camera with which the adapter and exposure control device must work is often the SX-70 Land Camera, which has an exposure control port located both laterally and vertically from the center of the camera's front lens when viewing the camera from the front. This has resulted in the complex structure typified by U.S. Pat. No. 3,976,368. Furthermore, this camera ejects the finished picture to the front of the camera when developed, and accordingly, the adapter and exposure control device involved must be compact and out of the way of the operating mechanism.